Formate dehydrogenase (EC.1.2.1.2) reduces NAD+ to reduced nicotinamide adenine dinucleotide (NADH) and oxidizes formic acid to carbon dioxide in the presence of oxidized nicotinamide adenine dinucleotide (NAD+), formic acid, and water. Based on the enzyme reaction, formate dehydrogenase is used for a system for regeneration of NADH from NAD+. Conventionally known examples of formate dehydrogenase include Candida boidinii (ATCC32195)-derived formate dehydrogenase as described in JP Patent Publication (Kokai) No. 2003-180383 A, NAD+-dependent-formate dehydrogenase from bacteria of the genus Bacillus as disclosed in JP Patent Publication (Kokai) No. 2002-233395 A, and Mycobacterium vaccae-derived formate dehydrogenase as disclosed in JP Patent Application No. H10-023896 (1998).
Also, the English translation of BIOCHEMISTRY (Moscow), Vol. 69, No. 11, 2004, pp. 1252-1267 (Biokhimiya, Vol. 69, No. 11, 2004, pp. 1537-1554) discloses formate dehydrogenase from various microorganisms or plants in addition to the above examples. However, as described in this document, the specific activity of formate dehydrogenase is not so significant compared with that of various enzymes. In other words, a method for producing NADH using a formate dehydrogenase reduction reaction to result in NADH can be said to result in poor productivity because of the low specific activity of formate dehydrogenase.
Various research findings regarding formate dehydrogenase have been accumulated to date, and functional alterations by site-directed mutagenesis have been reported (Biomolecular Engineering, 23, (2006) 98-110). However, all conventionally known formate dehydrogenases have low specific activity and low durability. Thus, the use of the formate dehydrogenase must be evaluated as insufficient for NADH production.